Space: Science & Technology
EISSN : 2692-7659
Published by: American Association for the Advancement of Science (AAAS) (10.34133)
Total articles ≅ 23
Latest articles in this journal
Published: 16 October 2021
Space: Science & Technology, Volume 2021, pp 1-13; https://doi.org/10.34133/2021/9846185
Tianwen-1, the first mission of China’s planetary exploration program, accomplished its goals of orbiting, landing, and roving on the Mars. The entry, descent, and landing (EDL) phase directly determines the success of the entire mission, of which the guidance, navigation, and control (GNC) system is crucial. This paper outlines the Tianwen-1 EDL GNC system design by introducing the GNC requirements followed by presenting the GNC system architecture and algorithms to meet such requirements. The actual flight results for the whole EDL phase are also provided in this paper.
Published: 12 October 2021
Space: Science & Technology, Volume 2021, pp 1-10; https://doi.org/10.34133/2021/9841456
The current interpretation technology of remote sensing images is mainly focused on single-modal data, which cannot fully utilize the complementary and correlated information of multimodal data with heterogeneous characteristics, especially for synthetic aperture radar (SAR) data and optical imagery. To solve this problem, we propose a bridge neural network- (BNN-) based optical-SAR image joint intelligent interpretation framework, optimizing the feature correlation between optical and SAR images through optical-SAR matching tasks. It adopts BNN to effectively improve the capability of common feature extraction of optical and SAR images and thus improving the accuracy and application scenarios of specific intelligent interpretation tasks for optical-SAR/SAR/optical images. Specifically, BNN projects optical and SAR images into a common feature space and mines their correlation through pair matching. Further, to deeply exploit the correlation between optical and SAR images and ensure the great representation learning ability of BNN, we build the QXS-SAROPT dataset containing 20,000 pairs of perfectly aligned optical-SAR image patches with diverse scenes of high resolutions. Experimental results on optical-to-SAR crossmodal object detection demonstrate the effectiveness and superiority of our framework. In particular, based on the QXS-SAROPT dataset, our framework can achieve up to 96% high accuracy on four benchmark SAR ship detection datasets.
Published: 28 September 2021
Space: Science & Technology, Volume 2021, pp 1-12; https://doi.org/10.34133/2021/9760520
In order to meet the requirements of the space environment for the lightweight and load capacity of the manipulator, this paper designs a lightweight space manipulator with a weight of 9.23 kg and a load of 2 kg. It adopts the EtherCAT communication protocol and has the characteristics of high load-to-weight ratio. In order to achieve constant force tracking under the condition of unknown environmental parameters, an integral adaptive admittance control method is proposed. The control law is expressed as a third-order linear system equation, the operating environment is equivalent to a spring model, and the control error transfer function is derived. The control performance under the step response is further analyzed. The simulation results show that the proposed integral adaptive admittance control method has better performance than the traditional method. It has no steady-state error, overcomes the problems caused by nonlinear discrete compensation, and can facilitate analysis in the frequency domain, realize parameter optimization, and improve calculation accuracy.
Published: 10 September 2021
Space: Science & Technology, Volume 2021, pp 1-8; https://doi.org/10.34133/2021/9763179
In this paper, a method of predicting the motion state of a moving target in the base coordinate system by hand-eye vision and the position and attitude of the end is proposed. The predicted value is used as the velocity feedforward, and the position-based visual servo method is used to plan the velocity of the end of the manipulator. It overcomes the influence of end coordinate system motion on target prediction in a discrete system and introduces an integral control method to compensate for the prediction velocity, eliminating the end tracking error caused by target velocity prediction error. The effectiveness of this method is verified by simulation and experiment.
Published: 3 September 2021
Space: Science & Technology, Volume 2021, pp 1-6; https://doi.org/10.34133/2021/9846852
It is still generally assumed that interstellar travel will be possible after purely technical development and thus that mankind can move to some suitable exoplanet when needed. However, recent research indicates this not to be the case, since interstellar space is filled with enough ultradense hydrogen H(0) as stable condensed dark matter (Holmlid, Astrophysical Journal 2018) to make interstellar space travel at the required and technically feasible relativistic velocities (Holmlid et al, Acta Astronautica 2020) almost impossible. H(0) can be observed to exist in space from the so-called extended red emission (ERE) features observed in space. A recent review (Holmlid et al., Physica Scripta 2019) describes the properties of H(0). H(0) gives nuclear processes emitting kaons and other particles, with kinetic energies even above 100 MeV after induction for example by fast particle (spaceship) impact. These high particle energies give radiative temperatures of 12000 K in collisions against a solid surface and will rapidly destroy any spaceship structure moving into the H(0) clouds at relativistic velocity. The importance of preserving our ecosystem is pointed out, since travel to suitable exoplanets may be impossible. The possibilities of instead clearing interstellar space from H(0) are discussed, eventually providing tunnels suitable for relativistic interstellar transport. Finding regions with low intensity of ERE could even be a way to identify space-cleaning activities and thus to locate earlier space-travelling civilizations.
Published: 28 August 2021
Space: Science & Technology, Volume 2021, pp 1-10; https://doi.org/10.34133/2021/9898756
On December 17, 2020, the Chang’e-5 reentry spacecraft landed safely and brought back the lunar sample without damage. This paper describes the recovery system that has critically contributed to the scientific success of the Chang’e-5 missions and presents the technical requirements and constraints of the recovery system for the Chang’e-5 reentry spacecraft and discusses the design process of the recovery system, including the system composition, working procedure, and some other key aspects. Finally, the ground cover rejection tests and air drop and flight tests were carried out to confirm the design configuration. The results showed that the Chang’e-5 reentry spacecraft recovery system was designed correctly, and its functions and performances met the design requirements. A breakthrough in the recovery technology of the reentry spacecraft was achieved for Chinese first lunar sample-return mission.
Published: 18 August 2021
Space: Science & Technology, Volume 2021, pp 1-10; https://doi.org/10.34133/2021/9874563
The paper presents a high-efficient finite difference method for solving the PDE model of the single-link flexible manipulator system with boundary feedback control. Firstly, an abstract state-space model of the manipulator is derived from the original PDE model and the associated boundary conditions of the manipulator by using the velocity and bending curvature of the flexible link as the state variables. Then, the second-order implicit Crank-Nicolson scheme is adopted to discretize the state-space equation, and the second-order one-sided approximation is used to discretize the boundary conditions with excitations and feedback control. At last, the state-space equation combined with the boundary conditions of the flexible manipulator is transformed to a system of linear algebraic equations, from which the response of the flexible manipulator can be easily solved. Numerical simulations are carried out to simulate the manipulator under various excitations and boundary feedback control. The results are compared with ANSYS to demonstrate the accuracy and high efficiency of the presented method.
Published: 13 August 2021
Space: Science & Technology, Volume 2021, pp 1-11; https://doi.org/10.34133/2021/9810375
Space debris, especially the space debris cloud, has threatened severely the safety of future space missions. In the framework of multibody system dynamics, a computational approach is proposed in this study to investigate the dynamics of net deployment and capture of space debris cloud using this net subject to large overall motions and large deformations. To obtain high simulation fidelity of capturing space debris cloud, the gradient deficient beam element of the absolute nodal coordinate formulation (ANCF) is employed to discretize threads which are woven into the net. The normal contact force between the net and the debris cloud and among debris particles is computed by using the penalty method. Some deployment examples are presented to investigate the influences of shooting velocity of bullets and microgravity as well as the angle between the traveling direction of the net and the microgravity direction on the deployment characteristics of the tethered net. Other capturing examples are given to clarify the effect of the deployment area of the net at the moment it starts to contact with the debris cloud on the capture rate and to demonstrate the effectiveness of the proposed approach for capturing space debris cloud using the net in microgravity conditions.
Published: 6 August 2021
Space: Science & Technology, Volume 2021, pp 1-9; https://doi.org/10.34133/2021/9807452
Visual perception provides state information of current manipulation scene for control system, which plays an important role in on-orbit service manipulation. With the development of deep learning, deep convolutional neural networks (CNNs) have achieved many successful applications in the field of visual perception. Deep CNNs are only effective for the application condition containing a large number of training data with the same distribution as the test data; however, real space images are difficult to obtain during large-scale training. Therefore, deep CNNs can not be directly adopted for image recognition in the task of on-orbit service manipulation. In order to solve the problem of few-shot learning mentioned above, this paper proposes a knowledge graph-based image recognition transfer learning method (KGTL), which learns from training dataset containing dense source domain data and sparse target domain data, and can be transferred to the test dataset containing large number of data collected from target domain. The average recognition precision of the proposed method is 80.5%, and the average recall is 83.5%, which is higher than that of ResNet50-FC; the average precision is 60.2%, and the average recall is 67.5%. The proposed method significantly improves the training efficiency of the network and the generalization performance of the model.
Published: 13 July 2021
Space: Science & Technology, Volume 2021, pp 1-15; https://doi.org/10.34133/2021/9823609
To achieve the goal of collecting lunar samples and return to the Earth for the Chang’E-5 spacecraft, the lander and ascender module (LAM) of the Chang’E-5 spacecraft successfully landed on the lunar surface on 1 Dec., 2020. The guidance, navigation, and control (GNC) system is one of the critical systems to perform this task. The GNC system of previous missions, Chang’E-3 and Chang’E-4, provides the baseline design for the Chang’E-5 LAM, and the new characteristics of the LAM, like larger mass and liquid sloshing, also bring new challenges for the GNC design. The GNC design for the descent and landing is presented in this paper. The guidance methods implemented in the powered descent are presented in detail for each phase. Propellant consumption and hazard avoidance should be particularly considered in the design. A reconfigurable attitude control is adopted which consists of the quaternion partition control, phase and gain stabilization filter, and dual observer. This controller could provide fast attitude maneuver and better system robustness. For the navigation, an intelligent heterogeneous sensor data fusion method is presented, and it is applied for the inertial measurement unit and velocimeter data. Finally, the flight results of the LAM are shown. Navigation sensors were able to provide valid measurement data during descent, and the thrusters and the main engine operated well as expected. Therefore, a successful soft lunar landing was achieved by the LAM.